1. Associate Professor, Dept. of Civil Engineering and Architecture (DICAr), Univ. of Catania at Siracusa, Piazza Federico di Svevia 1, I-96100 Siracusa, Italy.
2. Researcher, Dept. of Civil Engineering and Architecture (DICAr), Univ. of Pavia, Via Ferrata 3, I-27100 Pavia, Italy (corresponding author).